1. Field of the Invention
The present invention relates to a sulfur lamp. More particularly, the present invention relates to a sulfur lamp having electrodes, which eliminate the need to use a magnetron.
2. Description of the Background Art
There are various sources of lighting, e.g., an incandescent lamp using heat radiation, a fluorescent lamp including an electric discharge tube that uses a fluorescent material, a high intensity discharge (HID) lamp that uses an electric discharge within a high-pressurized gas or steam, and a plasma lighting system (PLS) lamp that uses an electrodeless discharge.
The various lamps have their respective advantages and disadvantages. For example, the incandescent lamp is excellent in color rendition and has a small size. However, the incandescent lamp is inefficient in emitting light and has a short life. Additionally a switching-on-light circuit of the incandescent lamp is simple and low-priced. The fluorescent lamp is efficient in emitting light and has a relatively long life. However, the fluorescent light has a relatively large size when compared to the incandescent lamp. Additionally, the fluorescent lamp requires a subsidiary switching-on-light circuit. The HID lamp is light-efficient and has a long life, but requires a relatively large amount of time between switching off and on light. In addition, the HID lamp, like the fluorescent lamp, requires a subsidiary light-switching circuit. The PLS lamp has a much longer life, when compared to the above-noted lamps, and is efficient in emitting light. Although low in power consumption, the PLS lamp is high-priced. In addition, the PLS lamp requires a subsidiary switching-on-light circuit.
The PLS lamp is among the latest lamps. An electrodeless sulfur lamp, which belongs to the family of PLS lamps, is a highly-efficient full-spectrum electrodeless lighting system whose light is generated by sulfur plasma that has been excited by microwave radiation. The electrodeless sulfur lamp consists of a golf-ball sized quartz bulb containing several milligrams of sulfur power and argon gas at the end of a thin glass spindle. The bulb is enclosed in a microwave-resonant wire-mesh cage. A magnetron bombards the bulb with 2.45 GHz microwaves. The microwave energy excites the gas to five times atmospheric pressure, which in turn heats the sulfur to an extreme degree forming a brightly glowing plasma capable of illuminating a large area. At an initial stage of switching on light, the discharge occurs in argon which is a buffer gas. As temperature increases, the discharge occurs in sulfurous steam, thereby emitting white light which is excellent in color rendition.
The first prototype of the electrodeless sulfur lamps were 5.9 kW units, having a system efficacy of 80 lumens per watt. The first production models were 1.4 kW with an output of 135,000 lumens. Later models were able to eliminate the need for a cooling fan and improve efficiency to more than 100 lumens/watt.
A problem with the conventional electrodeless sulfur lamp is that the life of magnetron is short-lived when compared to the quartz bulb. The design life of the quartz bulb is currently approximately 60,000 hours. However, the design life of the magnetrons are currently only about 15,000 to 20,000 hours. This requires frequent replacement of the life-expired magnetrons with new ones before the life of the quartz bulb expires. The development in the magnetron generating the micro-wave is relatively slow, which contributes to lowering an energy transfer rate.